The present invention relates to a device that detects the presence or absence of a charge quantity and stores the result.
Such a device is particularly used in charge transfer devices, specifically in filters which use charge transfer devices which are digitally programmable. In this type of filter, the M coefficients useful in the preparation of the transfer function of the filter, coded in a code with N bits, are stored in N charge transfer registers with M stages, called coefficient registers. The signal to be filtered is applied to the input of N other charge transfer registers with M stages, called signal registers. Each of the N signal registers is associated with one of the N coefficient registers (the size of the different signal registers increasing with the weight of the bits stored in the associated coefficient registers), and the stages of the same rank of each pair of registers formed in this way correspond.
A device for sensing or not sensing the charge transfer quantity obtained at the output of each of the stages of the signal register is associated with each pair of registers formed in this way, as a function of whether the bit stored in the corresponding stage of the associated coefficient register has the binary value 1 or the binary value 0.
A system of adders, supplying the output signal of the filter, is provided at the output of the different devices for counting the charge transfer quantity associated with the various signal register--coefficient register pairs.
A digitally programmable filter of this type is described in U.S. Pat. No. 4,316,258 assigned to Thomson-CSF.
Thus, there must be a device for detecting the presence or absence of the charge quantity obtained at the output of the considered stage of the coefficient register between the output of each of the stages of the different coefficient registers and the corresponding input of each of the different counting devices. The result of this detection conditions the operation of counting.
As the coefficients must also be stored during the processing of the signal, the device for detecting the presence or absence of the charge quantity must have a storage function. A device for detecting the presence or absence of a charge quantity and for storing the result thereof is described in U.S. Pat. No. 4,264,964 assigned to Thomson-CSF. This device is a semiconductor substrate on which are provided a group of electrodes controlled by periodic potentials.
These electrodes essentially consist of first and second electrodes, located in the extension of one another, and supplied from a first side, the first by the charge quantity to be detected and the second by a given charge quantity and from a second side by the charge quantity obtained at the output of a series of third electrodes arranged parallel to the two preceding electrodes, the first electrode of said series being supplied by a given charge quantity.
All these electrodes are controlled in such a way that initially the first and second electrodes are alternately blocked and conductive, thus permitting the introduction of a sample of the charge quantity to be detected. At the output of these two electrodes, either a signal having a virtually constant level, is obtained or a square signal depending on whether a charge quantity to be detected is present or absent, this makes it possible to make a distinction between the presence and absence of a charge quantity. Then, the first and second electrodes are simultaneously separated from their respective supplies located on the first side, permitting the storage of the result of the detection.
However, the construction of the device for detecting the presence or absence of a charge quantity described in the aforementioned U.S. Patent is such that the level of the square signal obtained at the output of the first and second electrodes when a charge quantity to be detected is present is identical to the constant level of the signal obtained at the same output when the charge quantity to be detected is absent. To maintain the distinction between the presence and absence of the charge quantity possible during the storage of the result of this detection, there is provided initially and when the charges to be detected are present an advance beneath the series of third electrodes of the given charge quantity present at the input of the first of them, from the first to the last of them, so as to subsequently produce a variation in the level of the output signal of the first and second electrodes in the case of the presence of the charge quantity to be detected.
The device for detecting the presence or absence of the charge quantity and for storing the result thereof described in the aforementioned patent has complex construction and operation, so that the control signals applied to the different electrodes are complex.